Raman induced soliton self-frequency shift in microresonator Kerr frequency combs

TL;DR

This paper reports the first observation of a Raman-induced soliton self-frequency shift in microresonator Kerr frequency combs, showing how the effect influences soliton spectra and can be tuned via pump parameters.

Contribution

It demonstrates the first experimental observation and theoretical description of Raman-induced shifts in microresonator solitons, enhancing understanding of Kerr comb dynamics.

Findings

Raman shift causes a red-shift in soliton spectra.

The shift is tunable via pump laser detuning.

The shift grows linearly with peak power.

Abstract

The formation of temporal dissipative solitons in continuous wave laser driven microresonators enables the generation of coherent, broadband and spectrally smooth optical frequency combs as well as femtosecond pulses with compact form factor. Here we report for the first time on the observation of a Raman-induced soliton self-frequency shift for a microresonator soliton. The Raman effect manifests itself in amorphous SiN microresonator based single soliton states by a spectrum that is hyperbolic secant in shape, but whose center is spectrally red-shifted (i.e. offset) from the continuous wave pump laser. The Raman induced spectral red-shift is found to be tunable via the pump laser detuning and grows linearly with peak power. The shift is theoretically described by the first order shock term of the material's Raman response, and we infer a Raman shock time of 20 fs for amorphous SiN. Moreover, we observe that the Raman induced frequency shift can lead to a cancellation or overcompensation of the soliton recoil caused by the formation of a (coherent) dispersive wave. The observations are in excellent agreement with numerical simulations based on the Lugiato-Lefever equation (LLE) with a Raman shock term. Our results contribute to the understanding of Kerr frequency combs in the soliton regime, enable to substantially improve the accuracy of modeling and are relevant to the fundamental timing jitter of microresonator solitons.